Browse Prior Art Database

Contacting Tunnel Junctions via Damascene Conducting Studs Fabricated using a Sacrificial Organic Dielectric

IP.com Disclosure Number: IPCOM000020077D
Original Publication Date: 2003-Oct-23
Included in the Prior Art Database: 2003-Oct-23
Document File: 7 page(s) / 84K

Publishing Venue

IBM

Abstract

Magnetic Random Access memories sense their bit values by the measuring the resistance offered to a tunneling current. This requires contacting through a top electrode. We discuss a method of fabricating such an electrode in a fashion that could reduce damage to the magnetic stack and increase across-the-wafer homogeneity.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 38% of the total text.

Page 1 of 7

  Contacting Tunnel Junctions via Damascene Conducting Studs Fabricated using a Sacrificial Organic Dielectric

Introduction

     Magnetic Random Access memories (MRAM) built using dense arrays of Magnetic Tunnel Junctions (MTJ) have been proposed as a universal memory. This is due to the potential they hold to non-volatility, high speed, density and endurance [1-2]. The MRAM bits require to be 'read' by sensing the different Tunnel magneto resistances offered by the device in its two logic. An integration scheme where the MTJs are positioned at the intersections of two mutually perpendicular arrays of word and bitlines is disclosed in prior art [3]. The Magnetic Stack however is a very thin (~ 100's of Angstroms) film. Standard Back end of line (BEOL) integration would not allow for successive metal levels to be placed within such proximity. This necessitates a conducting stud on top of the MTJs to serve as an electrical contact to the wordlines. We disclose herein a technique of fabricating such studs in a fashion that could be least damaging to the magnetic stack underneath.

Etch Uniformity and Corrosion Concerns

     The MTJ stack is a complex multi-layer film consisting of Ferromagnetic and other materials [4]. In order to protect the stack from corrosion, it is capped with a diffusion barrier such as Tantalum and its Nitrides (Ta or TaN) [4]. However subtractive etching of the contact stud often requires the use of corrosive gases such as Cl2 and BCl3. The lack of selectivity between the contact stud material (Thickness ~ 1000's A) and the cap TaN (Thickness ~ 10's of angstroms) and the disparity in thickness results in the corrosive chemistry coming in contact with the top layer of the MTJ stack. This problem is only exacerbated by any etch non-uniformity inherent to the etch tool since that further reduces the process window in overetch. An efficient contact stud definition process must hence target selective stopping on the cap TaN rather than on the magnetic layer.

Selective Stop on MTJ Cap

     It is well know to those skilled in the art that high selectivity against etching TaN can be achieved by the incorporation of Oxygen (O2) in the plasma discharge. Oxygen is known to passivate the surface of TaN by the formation of ceramic-like Tantalum Oxy-nitrides (TaON). These Tantalum oxide materials are known to have low sputter yield and hence a low etch rate in physical sputtering. Hence we propose the use of Oxygen based plasma in the formation of the contact stud. However, the metals desirable for the contact stud formation are neither etchable using oxygen plasma nor can one ensure selectivity against the photoresist mask used for patterning the contact stud. In order to circumvent these said drawbacks

1

Page 2 of 7

and yet have the benefits of a selective stop on the TaN during the Conductive Stud formation; we propose a damascene scheme.

Damascene Scheme using an Organic Dielectric

     Fig.1 illustrates the proposed integration scheme. We e...